<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <div class="box"></div>

    <script>
        const box = document.querySelector('.box');
        box.innerHTML='<strong>我是一个盒子</strong>'
    </script>
</body>
</html>